Lawyer Gerald Nissenbaum has been getting angry, wealthy people out of unhappy marriages for 40 years. Armed with details of financial portfolios and sexual perversions, the Boston-based divorce attorney commands upwards of $700 an hour and scores nine-figure settlements—or prevents them, depending on whom he's representing—for his wealthiest-one-percent clients. Now he dishes all (changing names, of course) in Sex, Love and Money: Revenge and Ruin in the World of High-Stakes Divorce. He shared some advice—and a few war stories:

MC: What are the dumbest mistakes people make when divorcing?

GN: They fail to get a good lawyer. And if there's a lover, they flaunt him, making their spouse act crazy, prolonging the process and costing them a bundle. They hide assets, which will be found—also extremely expensive. Or they put the kids in the middle, which just makes them heinous human beings.

GN: First of all, you are not in love with this person, so I strongly suggest you not tank your marriage over this folly. But if you must, then take pains to keep the relationship secret. We've learned from recent scandals not to use the cell phone to contact—call, text, or e-mail—a lover. But don't even take it with you to see him; it probably has a GPS chip, which can be subpoenaed. If you need to use a cell phone, buy a disposable one. Also, put your car's toll pass in an old-fashioned lead-lined film canister. Just taking it off the dashboard doesn't stop it from registering where you've been, and this information can be subpoenaed, too.

MC: What's the weirdest thing you ever saw at trial?

GN: I once asked a female client to describe her husband's abuse, and after running through the usual—name-calling, etc.—she breaks down and cries on the stand. The judge calls a recess, and I ask her what she isn't telling me. Turns out her husband liked porn, especially bestiality, and they had a German shepherd, and you can guess what he tried to make her do. We got her half of all his assets and very generous alimony.

MC: Are prenups for cynics?

GN: No, they're for people who come into marriages with assets they accumulated before they married, or people who want to make agreements about what is OK in their marriage. I had one couple make it official that neither could gain more than 15 pounds, because he didn't want to wind up with a fat wife, and she didn't want to wind up with a hypocrite.

MC: What about custody?

GN: That's the one thing you can't control. Even where there's a prenup, the state almost always decides custody. Brad and Angelina allegedly have an agreement that if they split up, she gets the kids. But that's worthless. The courts have total authority in matters of child welfare.